The invention relates to a motor vehicle wheel disc with arms, in particular for a passenger car, formed in one piece from embossed sheet metal, which represents an excellent compromise in terms of weight, cost, style or freedom of possible added styling (decorative wheel cover for example).
In the designing of a sheet metal wheel for a motor vehicle, the general aim is to optimise the weight and cost of such a product. The development of embossing techniques, numeric simulation means, and materials has led to great progress over the last few years. However, the majority of products has remained within the concept of a substantially axisymmetric disc (i.e. one whose cross-sectional profile is virtually fixed in form), comprising perforations and sometimes embossing in the upper part.
This type of profile does not give the product a very enhanced style or image, which explains in most cases why manufacturers resort to a decorative wheel cover placed on the product when it is mounted on the vehicle.
One can count several attempts to create style directly from the sheet metal forming the wheel disc by forming deep embossed areas forming stiffeners and/or a particular assembly of the disc with the rim (under-seat, “full-face” assembly, i.e. disc whose radially outer edge includes the outer flange and seat of the rim), with the rim welded at the end, etc. and sometimes associated with effects connected to painting. These attempts have not yet led to generalisation for reasons of excessive weight or difficulties in execution.
In general, the market for styled wheels for passenger cares is confined to the use of aluminium alloys. The process of manufacture (moulding, forging etc.) of these discs allows very broad freedom of style at reasonable weights, but has the disadvantage of being 4 to 8 (even 10) times more expensive.
The specification DE 201 08 995 U discloses a wheel whose disc is formed from a single piece of embossed sheet metal, with an inner face and an outer face. This disc has a radially outer circular mounting part intended to be connected to a rim, a radially inner part for fixing and centering to a wheel hub with a bearing area having a given number of fixing apertures and ending radially inwardly with an edge which is turned axially outwardly or centering apertures, and spokes or radial arms connecting the inner and outer parts, each spoke being disposed substantially circumferentially between two adjacent fixing apertures and the radially inner free edges of the radially outer circular part defining perforations with the free lateral edges of the spokes. This disc has a substantially circular, plane bearing region and each spoke comprises two lateral stiffening elements which extend radially from the bearing area to the radially outer circular assembly part and are disposed on either side of an intermediate strip axially receding towards the exterior of the disc.
Although freedom of styling either bare or with an attached part (decorative wheel cover for example) is apparently obtained, such a disc has the disadvantage of requiring a relatively thick sheet metal to be able to withstand the forces to which it is subjected during operation, in particular in the joining region between the spokes and the radially inner part for fixing and centering the disc.
Hereinafter:
the “internal face” of the disc shall refer to the side of the disc oriented inwards, in particular the internal face of the bearing region is intended to come into contact with the outer surface of the wheel hub to which the disc is to be fixed;
the “external face” of the disc, to the side of the disc oriented outwards, which side is visible when the wheel is mounted on the vehicle.
The object of the invention is a similar wheel disc in which, in order to reinforce each spoke mechanically, the central region of each of the arms or spokes is deformed in order to house a swelling axially receding relative to the lateral regions of the spokes of the disc, the swelling extending radially from the centering aperture, including a yoke of the radially inner fixing and centering part, along the central part of the spokes and as far as the outer circular mounting part and in which the yoke is offset axially outwardly relative to the bearing region.
The particular geometry of the radially inner part for fixing and centering the disc has the advantage of reducing the stress peaks withstood by this region during operation.
According to an advantageous embodiment, and taking into account a median axial plane between two adjacent fixing apertures, the axial distance (e) separating the internal face of the yokes and the internal face of the bearing region is at all points greater than the initial thickness of the sheet metal forming the wheel disc.
According to a preferred embodiment, the spokes have free lateral cut-out edges turned down towards the inner face of the disc. In the same way, advantageously the radially inner free edges of the circular assembly part are turned towards the inner face of the disc.
According to another preferred feature of the invention, the edges of the perforations are obtained by cutting out sheet metal, then turning down towards the inner face of the disc. This has the advantage of releasing a maximum perforated area so that no cut-out face is visible from the outside.
On the other hand, the appearance thus obtained is pleasant and the heavy perforation, apart from aerating the brakes well, brings a large degree of freedom of added styling (decorative wheel cover).
Preferably, the widths and depths of the swellings as well as the widths, sections and bending resistance of the spokes in the circumferential direction may decrease continuously from the radially inner part towards the radially outer circular part.